(CNN) -- The man in front of me clasping a new satellite telephone tells me he has an urgent message. He's just received a call from his hometown warning him Moammar Gadhafi's forces are on the verge of overrunning it and he's desperate for NATO to do something about it.

Mohammed, as he wants to be known, is a middle-aged, middle-class professional.

He says he walked out of al Galaa, population 16,000, under cover of darkness three weeks ago on a harrowing two-night trek to break the siege and bring word of their suffering. It's been his mission ever since, and tonight is no exception.

"The shelling has increased," he tells me.

Libyan leader Gadhafi's forces have the hilltop "surrounded" and have "switched to 106mm rockets" that he tells me are reaching their targets more effectively than the Grad and Katusha missiles they've been firing for the past two months.

Al Galaa is in the Nafusa mountains, about 129 kilometers (80 miles) from the capital Tripoli. It sits on a small plateau next to Yefren, a town of similar size. They are at the eastern tip of a slender sliver of rebel-held territory extending 270 kilometers (168 miles) westwards to the Tunisian border. Both have been targeted by Gadhafi since they joined the rebellion three months ago.

In that time, according to Mohammed, townspeople have had their water poisoned, their houses destroyed by shelling, been shot at, arrested, denied hospital treatment and even used as human shields.

Since arriving in the rebel stronghold of Zintan about 40 kilometers (25 miles) away, Mohammed has sent a satellite phone back to the rebels he left behind. That's how he says he stays on top of news from there.

He tells me Gadhafi's forces have taken control of the west of Yefren, including the hospital, the bank and the shops. What remains of the population, he says, are huddled in the east of Yefren, in al Galaa and in nearby caves.

Most of the 32,000 estimated residents fled about two months ago, he says. He says it's impossible to know exactly how many people are left but guesses it's about 1,000, half of them rebels, half of them civilians.

He claims they have been out of electricity and water for seven weeks and there is no access to the hospital, but what worries him most is Gadhafi's switch to 106mm rockets. He says it's now or never for NATO.

If they are serious, he says, "they could end the siege in two hours."

When I ask what he means, he explains the rebels have tried blowing up the two roads that lead to the mountain top without success. "All they need to do is blow up the roads to stop Gadhafi's advance."

Every day, he says, he calls in the latest coordinates of Gadhafi's forces to the rebel command in Benghazi. Each day with no NATO action, he says he can only hope his details are being passed along correctly. "Look at Benghazi and Misrata," he says. "Gadhafi's forces were stopped by NATO bombing, why not here in Yefren and al Galaa?"

It's impossible for us in Zintan to verify Mohammed's accounts. He says he could take us there but the several-day hike through the mountains would be incredibly dangerous and could end in disaster.

Zintan's rebel commander says he's getting no new information from Yefren and fears it may already be lost to Gadhafi's forces. According to a Libyan doctor at Zintan's hospital, four men arrived from al Galaa a few days ago.

They had walked for two days, they told him, taken the same nighttime route as Mohammed. One had a broken arm, the doctor said. It had been set in hardened henna because doctors had run out of regular bandages. Their stories he told me matched Mohammed's dire warning.